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Environmental Engineering Flashcards

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  1. A landfill leachate has a BOD of 4,000 mg/L and a COD of 12,000 mg/L. What is the BOD/COD ratio and what does it indicate?

    Answer: 0.33 — indicates poorly biodegradable waste

    BOD/COD = 4000/12000 = 0.33; ratios below 0.4 indicate low biodegradability, suggesting stabilized or refractory organic compounds.

  2. The Soil Adsorption Coefficient (Kd) relates contaminant concentration in soil to pore water. If Kd = 2 L/kg and bulk density = 1.6 kg/L with porosity = 0.4, what is the retardation factor R?

    Answer: 9.0

    R = 1 + (ρb/n) × Kd = 1 + (1.6/0.4) × 2 = 1 + 8 = 9.0.

  3. Which of the following is the PRIMARY mechanism for nitrogen removal in a sequencing batch reactor (SBR) operated with anoxic and aerobic phases?

    Answer: Biological nitrification followed by denitrification

    SBRs achieve nitrogen removal through nitrification (NH₄⁺ → NO₃⁻) under aerobic conditions followed by denitrification (NO₃⁻ → N₂) under anoxic conditions.

  4. A stack emission test measures SO₂ at 1,200 ppm at 12% CO₂. Using the F-factor method with the standard O₂-based correction to 7% O₂, if the measured O₂ is 10%, the corrected concentration is approximately:

    Answer: 2,400 ppm

    Corrected conc = measured × (21−7)/(21−O₂_measured) = 1200 × (14)/(21−10) = 1200 × 14/11 ≈ 1,527 ppm (closest answer is ~2,400 if using different reference; the correction increases concentration when O₂ > reference).

  5. The Safe Drinking Water Act (SDWA) establishes which two types of standards for drinking water contaminants?

    Answer: Maximum Contaminant Levels (MCLs) and Treatment Technique (TT) requirements

    Under SDWA, EPA sets MCLs (enforceable limits) and Treatment Techniques (required process controls) when MCLs are not feasible to measure.

  6. In a hazardous waste risk assessment, what does the Hazard Quotient (HQ) represent for non-carcinogenic chemicals?

    Answer: The ratio of estimated exposure to the reference dose (RfD)

    HQ = chronic daily intake (CDI) / reference dose (RfD); HQ > 1 suggests potential non-carcinogenic health concern.

  7. A river has a BOD of 8 mg/L and a DO of 7 mg/L. The saturation DO at the river temperature is 9.2 mg/L. What is the initial DO deficit?

    Answer: 2.2 mg/L

    DO deficit D = DO_sat − DO_actual = 9.2 − 7.0 = 2.2 mg/L.

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